a. Field of the Invention
The invention relates to a dual lamp illumination system, and particularly to a dual lamp illumination system having varifocal lenses.
b. Description of the Related Art
FIG. 1 shows a schematic diagram of a dual lamp illumination system 100 disclosed in U.S. Pat. No. 7,182,468. As shown in FIG. 1, an integration rod 106 receives emitting light of a left-side light source 102 and guides the light into another integration rod 110, and an integration rod 108 receives emitting light of a right-side light source 104 and also guides the light into the same integration rod 110. Hence, the light beam from different light sources are combined together and then propagate in the same direction. However, the emitting light of the left-side light source 102 goes into the integration rod 110 via a first entrance equal to half of an light incident surface of the integration rod 110, and the emitting light of the right-side light source 104 goes into the integration rod 110 via a second entrance equal to the remaining half of the light incident surface of the integration rod 110. Hence, a light collection angle and a light collection area of the integration rod 110 fail to be increased to result in inferior light collection efficiency. Accordingly, another conventional design is proposed to solve the problem.
Referring to FIG. 2, U.S. Pat. No. 7,201,498 discloses a dual lamp illumination system 200 that includes light sources 202 and 204, light-combining lens assembly 206, and a movable reflective prism 208. However, though the effect of combining light beams transmitted from different directions is optimized through the movement of the reflective prism 208, the light collection angle fails to be further increased to improve luminous efficiency. Besides, referring to FIG. 3, Taiwan patent publication no. 200743822 discloses a dual lamp illumination system 300 that includes a light-combining prism 302, light sources 304 and 306, and condenser lenses 312, 314 and 316. The light-combining prism 302 reflects emitting light beam of light sources 304 and 306, and the condenser lenses 312, 314 and 316 are allowed to enhance the effect of combining light beams from the light sources 304 and 306. Similar designs are disclosed, for example, in U.S. Pat. No. 6,224,217 and U.S. Pat. No. 7,125,144, where each illumination system includes a light-combining prism and a lens assembly. However, such designs fail to achieve optimum luminous efficiency and output brightness, when only one lamp in a dual lamp illumination system is turned on.